Process for the production of neutral-tasting pastes of alkyl ether sulfates in glycerol

ABSTRACT

Process for the production of a neutral-tasting paste of an alkyl ether sulfate in glycerol, comprising the steps of: 
     A) forming an aqueous paste of at least one alkyl ether sulfate wherein the aqueous paste contains from about 25 to about 75% by weight of alkyl ether sulfate; 
     B) adding glycerol to the aqueous paste from step A) in from about 1 to about 4 times the quantity by weight of the aqueous paste; 
     C) distilling off substantially all of the water present in the mixture resulting from step B) to produce a substantially ambydrous paste; and 
     D) passing steam heated to a temperature above 100° C. through skid paste with intensive whirling of the paste and steam phases.

this application is a 371 of PCT/EP92/02073, filed Sep. 8, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the production ofneutral-tasting pastes of alkyl ether sulfates in glycerol.

2. Statement of Related Art

In contrast to alkyl sulfates, alkyl ether sulfates have hardly everbeen used in toothpastes on account of their unpleasant taste andaftertaste.

It is known from German patent application DE 30 44 481 that 1,4-dioxanecan be removed from water-containing pastes of alkyl ether sulfates inadmixture with water by azeotropic evaporation. DE-OS 34 47 867describes a process for the removal of 1,4-dioxane from alkyl ethersulfates, in which an ethoxylated silicone oil is added to thewater-containing surfactant paste for defoaming purposes and steam issubsequently passed through the resulting mixture. These processes givewater-containing pastes of alkyl ether sulfates which, by virtue oftheir reduced 1,4-dioxane content and the lower danger potentialresulting therefrom, may be used with advantage in detergents andcleaning preparations.

However, distillation-based operations involving water-containing alkylether sulfate pastes of relatively high concentration are complicated bythe presence of gel phases. Accordingly, there is a need for processeswhich enable unwanted secondary products to be removed from alkyl ethersulfate pastes. These secondary products are only present in lowconcentrations and, as in the case of taste-forming or odor-emittingsubstances for example, are generally not known in their entirety.

DESCRIPTION OF THE INVENTION

The problem addressed by the present invention was to provide a processfor the production of neutral-tasting pastes of alkyl ether sulfates.

According to the invention, this problem has been solved by a processfor the production of neutral-tasting pastes of alkyl ether sulfates inglycerol, in which

(a) glycerol is added to an aqueous paste containing 25

to 75% by weight of an alkyl ether sulfate in a 1-to 4-fold excess byweight, based on the aqueous alkyl ether sulfate paste, and the waterpresent is distilled off substantially completely from the mixture atelevated temperature and

(b) steam heated to temperatures above 100° C. is passed through themixture obtained in this way with intensive whirling of the liquid andsteam phases.

In the context of the invention alkyl ether sulfates are the sulfates ofadducts of ethylene oxide (EO) and/or propylene oxide (PO) withsaturated and/or unsaturated, linear and/or branched fatty alcoholsobtainable by known methods. The fatty alcohols on which the alkyl ethersulfates are based may be pure compounds. However, it is normallypreferred to use mixtures of different fatty alcohols obtained fromnative raw materials, such as fats and oils. These fatty alcohols may bereacted with the alkylene oxides, for example under pressure and in thepresence of catalysts, to form fatty alcohol alkoxylates.

It may stated with regard to the degree of alkoxylation thatalkoxylation reactions such as, for example, the addition of x moles ofethylene oxide onto 1 mole of fatty alcohol by known methods ofethoxylation do not give an adduct per se, but rather a mixture ofresidues of free fatty alcohol and a number of homologous (oligomeric)addition products of 1, 2, 3, . . . x, x+1, x+2 . . . etc. molecules ofethylene oxide per molecule of fatty alcohol. The average degree ofethoxylation (x) is defined by the starting quantities of fatty alcoholand ethylene oxide. The distribution curve of the homolog mixturegenerally shows a maximum in the range from x-3 to x+3. Furtherinformation on this subject can be found, for example, in the JournalSoap/Cosmetics/Chemical Specialties, Jan. 1988, page 34.

The desired alkyl ether sulfates are ultimately obtained by reaction ofthe fatty alcohol alkoxylates with, for example, sulfur trioxide orchlorosulfonic acid and subsequent neutralization, for example withalkali metal, alkaline earth metal, aluminium or ammonium hydroxides.

Preferred alkyl ether sulfates are compounds corresponding to formula(I):

    R--O--(C.sub.n H.sub.2n O).sub.x --SO.sub.3 M              (I)

in which R is a saturated or olefinically unsaturated, linear orbranched C₈₋₂₂ alkyl radical, n is the number 2 or 3, x is a number of 1to 15 and M is hydrogen, an alkali metal, an alkaline earth metal,aluminium, an ammonium group or an alkyl or alkylol ammonium groupcontaining 1 to 4 carbon atoms in each alkyl or alkylol group.

Particularly preferred compounds are those in which R is a saturatedC₈₋₁₆ alkyl radical, n=2, x is a number of about 2 to 10 and M issodium, potassium, magnesium, aluminium, ammonium or a mono-, di- ortriethanolammonium group.

Step (a) of the process according to the invention is carried out usingin particular aqueous pastes containing 30 to 70% by weight andpreferably 55 to 70% by weight of an alkyl ether sulfate.

The pastes of alkyl ether sulfates in glycerol obtained by the processaccording to the invention still contain water from the steam treatmentand may be used as such. However, it may be desirable to reduce theirwater content, for example by distillation. For practical reasons, watercontents below 3% by weight have proved to be favorable.

The neutral-tasting pastes of alkyl ether sulfates in glycerol accordingto the present invention are suitable for use in the cosmetics field.Thus, cosmetic preparations where it is important to avoid any adverseeffect on taste, for example toothpastes, can be produced on the basisof the pastes according to the invention.

The following Examples are intended to illustrate the invention withoutlimiting in any way.

EXAMPLES

l. Substances used

Texapon N 70: aqueous solution of sodium lauryl ether sulfate; activesubstance content: approx. 70% by weight ("Texapon®N70"; Henkel KGaA,Dusseldorf)

Glycerol: 99% (Henkel KGaA, Dusseldorf)

Dehydazol A 400 P: carboxymethyl cellulose, Na salt (Henkel KGaA)

Sident 12 DS: silica, precipitated (Degussa AG)

Syloblanc 34 (Sn 34): silica, amorphous (Grace)

Example 1

A mixture of 100 g of Texapon N70 and 400 g of glycerol was introducedinto a stirred vessel and the water present therein was removed bydistillation first at 80° C./100 torr and then at 110° C./20 torr. Steamwas then passed through the paste obtained for 2.5 hours at 120° C./12torr, followed by drying for 30 minutes at 120° C./5 torr. The watercontent of the resulting paste of Texapon N 70 in glycerol was 0.3% byweight.

Example 2

Toothpaste formulations A and B (see Table 1) were prepared to test thetaste properties of the alkyl ether sulfate produced by the processaccording to the invention in comparison with the correspondinguntreated alkyl ether sulfate.

                  TABLE 1                                                         ______________________________________                                                       Formulation A Formulation B                                    Constituent    % by weight   % by weight                                      ______________________________________                                        Dehydazol A 400 P                                                                            1.2           1.2                                              Sident 12 DS   21.0          21.0                                             Syloblanc 34 (Sn 34)                                                                         1.0           1.0                                              Glycerol 86%   25.0          25.0                                             Sorbitol 70%   15.0          15.0                                             NaF             0.22          0.22                                            Saccharin Na   0.1           0.1                                              Flavoring oil  1.0           1.0                                              TiO.sub.2      1.0           1.0                                              Preservative   0.1           0.1                                              Texapon N70.sup.a)                                                                           2.0           --                                               (acc. to Example 1)                                                           Texapon N70.sup.a)                                                                           --            2.0                                              (untreated)                                                                   Water, dist.   ad 100        ad 100                                           ______________________________________                                         .sup.a) In % by weight of active substance                               

Result:

Formulation A which contained alkyl ether sulfate pretreated by theprocess according to the invention was substantially neutral in itstaste while formulation B which contained the untreated alkyl ethersulfate had a pronounced taste and aftertaste.

We claim:
 1. A process for the production of a neutral-tasting paste ofan alkyl ether sulfate in glycerol, comprising the steps of:A) formingan aqueous paste of at least one alkyl ether sulfate wherein the aqueouspaste contains from about 25 to about 75% by weight of alkyl ethersulfate; B) adding glycerol to the aqueous paste from step A) in fromabout 1 to about 4 times the quantity by weight of the aqueous paste; C)distilling off substantially all of the water present in the mixtureresulting from step B) to produce a substantially anhydrous paste; andD) passing steam heated to a temperature above 100° C. through saidpaste with intensive whirling of the paste and steam phases.
 2. Theprocess of claim 1 wherein in step A) the aqueous paste contains fromabout 30 to about 70% by weight of alkyl ether sulfate.
 3. The processof claim 2 wherein the aqueous paste contains from about 55 to about 70%by weight of alkyl ether sulfate.
 4. The process of claim 1 wherein theat least one alkyl ether sulfate in step A) is derived from a mixture offatty alcohols obtained from a native fat or oil.
 5. The process ofclaim 1 wherein the at least one alkyl ether sulfate in step A) is atleast one alkyl ether sulfate of, the formula:

    R--O--(C.sub.n H.sub.2n O).sub.x --SO.sub.3 M              (I)

in which R is a saturated or olefinically unsaturated, linear orbranched C₈₋₂₂ alkyl radical, n is the number 2 or 3, x is a number offrom about 1 to about 15, and M is hydrogen, an alkali metal, analkaline earth metal, aluminum, an ammonium group or an alkyl or alkylolammonium group containing 1 to 4 carbon atoms in each alkyl or alkylolgroup.
 6. The process of claim 5 wherein in the alkyl ether sulfate offormula I, R is a saturated C₈₋₁₆ alkyl radical, n=2, x is a number offrom about 2 to about 10, and M is sodium, potassium, magnesium,aluminum, ammonium or a mono-, di- or triethanolammonium group.
 7. Theprocess of claim 1 wherein following step D) water is removed from thepaste until the paste has a water content of less than 3% by weight. 8.A toothpaste composition containing a surfactant effective quantity ofthe neutral-tasting paste prepared by the process of claim
 1. 9. Atoothpaste composition containing a surfactant effective quantity of theneutral-tasting paste prepared by the process of claim 5.